From: Dave Hansen Subject: Re: [PATCH] NFSD: fix wrong mnt_writer count in rename (MMOTM 2007-11-10-19-05) Date: Tue, 13 Nov 2007 09:39:41 -0800 Message-ID: <1194975581.7078.144.camel@localhost> References: <200711130115.lAD1FBfG015626@agora.fsl.cs.sunysb.edu> Mime-Version: 1.0 Content-Type: text/plain Cc: bfields@fieldses.org, Andrew Morton , linux-kernel@vger.kernel.org, nfs@lists.sourceforge.net To: Erez Zadok Return-path: In-Reply-To: <200711130115.lAD1FBfG015626@agora.fsl.cs.sunysb.edu> Sender: linux-kernel-owner@vger.kernel.org List-ID: On Mon, 2007-11-12 at 20:15 -0500, Erez Zadok wrote: > NFSD forgets to call mnt_drop_write after a successful rename. Here's a > fix. (Ah, the curse of a stackable file system developer: you have to debug > everyone else's too. :-) > > One thing I wasn't sure is whether I could move the mnt_drop_write line a > little above, just after the call to vfs_rename. If we can drop the ref > earlier, it could improve scalability/performance just a bit, no? (i.e., > what are the ramifications of holding on to this mnt writer ref longer than > needed?) I do see some write-ish things happening inside of the nfsd_sync_dir() call chain: the fsync() and filemap_fdatawrite(). The danger here is that the moment you mnt_drop_write(), the filesystem is mounted r/o by someone else, then those fsync() writes occur when everyone thinks it is r/o. So, I think your fix is the most conservative, and the most correct. > Signed-off-by: Erez Zadok > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > index 7dfde65..47aec49 100644 > --- a/fs/nfsd/vfs.c > +++ b/fs/nfsd/vfs.c > @@ -1693,6 +1693,7 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen, > if (!host_err) > host_err = nfsd_sync_dir(fdentry); > } > + mnt_drop_write(ffhp->fh_export->ex_path.mnt); > > out_dput_new: > dput(ndentry); Otherwise, looks good to me. Thanks. Signed-off-by: Dave Hansen -- Dave